1. Field of the Invention
This invention relates to a hybrid fiber-reinforced plastic composite material having excellent mechanical properties composed of a plastic matrix and as a reinforcing material, hybrid fibers consisting of inorganic fibers composed mainly of silicon, either titanium or zirconium, carbon and oxygen and at least one kind of fibers selected from the group consisting of carbon fibers, glass fibers, boron fibers, aramide fibers and silicon carbide fibers having a carbon core.
2. Description of the Prior Art
Research work has been under way on hybrid fiber-reinforced plastic composite materials which contain at least two kinds of fibers in the matrix as a reinforcing material in order to utilize the properties of the individual materials. For example, carbon/glass fibers, carbon/aramide fibers (Kevlar), boron/carbon fibers, boron/Kevlar fibers, boron/glass fibers, ceramic/Kevlar fibers and Kevlar/glass fibers have been studied as hybrid fibers for reinforcing such plastics as epoxy resins, modified epoxy resins, polyester resins and polyimide resins. The carbon/glass and carbon/Kevlar combinations have been most studied and gained practical applications.
When carbon fibers are used, their surface must be treated because their wettability with resins is inferior. A composite material obtained by using surface-treated carbon fibers, however, has a low interlayer shear strength and a low tensile strength in a direction perpendicular to the fibers. Hence, the fibers are liable to come off, and the composite material has a low fatigue strength and a low flexural impact value. Hence, the composite material is susceptible to fracture. With glass fibers, a sufficient reinforcing effect cannot be obtained because of their low tensile strength and modulus. Boron fibers and silicon carbide fibers having a carbon core cannot be used in bent portions of a complex shape because of their large diameters. Aramide fibers are weak to compression, and a composite material obtained by using them has low fatigue resistance.
According to this invention, specific inorganic fibers composed mainly of silicon, either titanium or zirconium, carbon and oxygen are used as one component of the hybrid fibers. Since these inorgnaic fibers have high strength of bonding to plastics and superior flexibility, they can be easily spun, and make up for the inherent defects of the other fibers described above and thus increase the reinforcing effect of these fibers. One example of applying the inorgnic fibers used in this invention as a plastic reinforcing material is described in Japanese Patent Application No. 11134/1985.